Pressure gauges are used in manufacturing processes, such as in the semiconductor manufacturing industry, to indicate the pressure of liquids or gases contained within fluid or gas handling devices, such as pipes, heat exchanges, pumps and the like. Such pressure gauges are commonly coupled to pressure gauge protection which separate the process fluid from the gauge. Pressure gauge protection generally comprise a diaphragm-type housing that is attached at one end to a nipple or fitting on the fluid handling device and at its other end to the pressure gauge. The diaphragm housing conventionally includes an inlet opening at one end that is attached to the pipe fitting and which permits the passage of process fluid into the housing. A diaphragm is disposed with the housing and defines two chambers within the housing, a first chamber extending from the inlet opening to one surface of the diaphragm, and a second chamber extending from a gauge end of the housing to an opposite surface of the diaphragm. A liquid pressure transfer medium, such as distilled water and the like, is typically contained in the second chamber between the diaphragm surface and a pressure gauge connected to the housing gauge end.
Process fluid leaving the pipe and entering the inlet opening contacts the surface of the diaphragm, causing the diaphragm to move in a direction towards the gauge end. Movement of the diaphragm in response to the process fluid acting on it causes a pressure to be exerted by the opposite diaphragm surface to pressurize the liquid pressure transfer medium, which pressure is indicated by the pressure gauge. A diaphragm-type gauge protector constructed in this manner serves to protect the pressure gauge from the potentially harmful effects of caustic or corrosive process chemicals.
However, the above-described single diaphragm-type gauge protector has certain deficiencies. The use of a single diaphragm construction provides a relatively accurate pressure transfer from the process fluid to the liquid pressure transfer medium at lower pressures, where unwanted deformation of the diaphragm is unlikely, i.e., deformation of the diaphragm which does not result in equivalent pressure transfer to the liquid pressure transfer medium.
Additionally, the above-described diaphragm-type gauge protector which uses water as a transfer medium cannot be used in applications where the process fluid temperature is greater than or equal to about 100.degree. C., i.e., at or above the boiling point of water. When process fluid at or above 100.degree. C. enters the gauge protector housing, the temperature of the water rises to its boiling point. This introduces vapor bubbles into the pressure transfer medium which causes inaccuracies in the indicated pressure due to the compressibility of the bubbles. Additionally, heating the water pressure transfer medium to above its boiling point results in a dramatic increase in the volume of the transfer medium which could cause diaphragm to rupture, thereby placing the pressure gauge in contact with potentially corrosive or caustic process chemicals. Rupturing of the diaphragm could also introduce the liquid pressure transfer medium into the process fluid, thereby, contaminating the fluid or gas processing system and, thereby, possibly causing damage to the particular product being manufactured, e.g., a large number of semiconductor chips.
Process fluids that are typically used in semiconductor manufacturing include either strong acids or strong bases that are elevated to temperatures near their boiling point to increase their effectiveness in an etching process. To accommodate use in such high-temperature applications single diaphragm-type gauge protectors have been modified by replacing the water pressure transfer medium with a higher boiling point liquid, such as oil and the like. Although application of the above-described diaphragm-type gauge protecting apparatus, comprising a high boiling point liquid pressure transfer medium, permits such apparatus to be used without the possibility of boiling the liquid pressure transfer medium, the use of the gauge protector in such an application places the diaphragm in contact with such chemicals at elevated temperatures. Placing the diaphragm in direct contact with such chemicals and under such conditions increases the likelihood of diaphragm rupture by both chemical attack and by mechanical thermally related failure. A diaphragm rupture in such an application may cause damage to the pressure gauge by exposure of the gauge to the corrosive chemicals, and may cause danger to the surrounding environment or a heath risk to nearby operators if the process liquid is allowed to exit the gauge protector and enter the environment.
Additionally, in the process of manufacturing semiconductors, it is desired that the chemicals used in the manufacturing process be of high purity to ensure that the manufactured product, a semiconductor chip, be without defects. A diaphragm rupture in such application could, therefore, cause the liquid pressure transfer medium, e.g., oil, to enter the process handling system and contaminate the process chemicals, the process handling devices, and semiconductors manufactured using such contaminated process chemicals. Accordingly, potential damage caused from such a diaphragm rupture could be quite costly. It is, therefore, desirable that a gauge protector be constructed that will facilitate accurate process pressure monitoring under conditions of both low and high pressure and of high temperature. It is desirable that a gauge protector be constructed in a manner that will eliminate the potential for pressure gauge damage or fluid handling system contamination caused by diaphragm rupture in high-temperature applications. It is also desirable that the gauge protector be constructed using conventional manufacturing methods from conventional and available materials.